Field of the Invention
Embodiments of the present invention relate generally to laser-based image-generating systems and, more specifically, to systems for producing 2-D straight-line scanning on an imaging surface using a raster polygon and a method of forming the same.
Description of the Related Art
In laser-based image-generating systems, a rotating polygon mirror is commonly used to scan one or multiple laser beams across an image-generating surface, such as the light-sensitive drum of a laser photo-copier or the phosphor screen of a laser-phosphor display. A rotating polygon mirror is a multi-faceted optical element having a plurality of reflective surfaces. A laser beam incident on one of the reflective surfaces is directed to the image-generating surface, and as the polygon rotates, the incident laser beam sweeps across the image-generating surface, thereby producing one line of an image on the image-generating surface.
In some devices, a specialized rotating polygon mirror, known as a raster polygon mirror, is used to produce 2-dimensional scanning of lasers across the image-generating surface. In a raster polygon mirror, each reflective surface is canted at a different angle. As with a rotating polygon mirror, when the raster polygon mirror rotates, a laser beam incident on a reflective surface of the raster polygon beam sweeps across the image-generating surface to produce a line of an image on the image-generating surface. However, as each subsequent reflective surface rotates through the incident laser beam, the beam is directed to and sweeps across a different location on the image-generating surface, thereby performing 2-dimensional scanning of the laser across the image-generating surface. Thus, a raster polygon mirror allows a laser to be scanned across a 2-dimensional surface using a single moving component, thereby facilitating high-speed laser imaging technologies.
A drawback to using a raster polygon mirror for scanning lasers across an image-generating surface is that the lasers so directed do not follow straight lines across the image generating surface. Instead, the scan lines of the lasers have significant curvature, which greatly complicates image processing and timing. In addition, each distinct canted reflective facet of a raster polygon mirror produces a corresponding distinct curvature, producing noticeable and undesirable distortion of images produced on the image-generating surface, as illustrated in FIG. 1. FIG. 1 illustrates curved laser scan lines 101-109 produced on an imaging surface 99 by a prior art laser scanning system using a single laser beam directed to a raster polygon mirror. As shown, rather than being straight and parallel lines, laser scan lines 101-109 are arcs. Because each of laser scan lines 101-109 is produced by a different reflective facet of the raster polygon mirror rotating through the incident laser beam, and because each reflective facet produces a different degree of distortion, each of laser scan lines 101-109 is an arc with different curvature. Such distortion is primarily caused by asymmetrical rotation properties of the different reflective facets and by distortion of the scan-imaging optics that focus the laser on the imaging surface. Such distortion of laser scan lines 101-109 is generally visible to a viewer and can result in a degraded viewing experience.
As the foregoing illustrates, there is a need in the art for a laser-scanning system that produces straight and parallel laser scan lines on an image-generating surface using a raster-scanning polygon mirror.